In conventional image processing circuits, it has been necessary to raise the operating speeds of an analog to digital converter, a memory control circuit and other circuits as the frequencies of the video signals have been increased, since the video signals are analog to digital converted using a picture element clock. Conventionally, for sampling those signals of high frequencies, it has been proposed to use a method for sampling the signals in a plurality of fields as disclosed in Japanese Patent Application Disclosure Gazette (kokai) No. SHO. 61-157029 or a method for sampling the signals by using a plurality of analog to digital converters as disclosed in Japanese Patent Application Disclosure Gazette (kokai) No. SHO. 63-125020, in order to lower the operating speed of the analog to digital converter. In addition, a video printer which permits processing of high definition still pictures has been described in Japanese Patent Application Disclosure Gazette (kokai) No. HEI. 2-67883.
An apparatus which permits only one video input unit, such as a TV camera, to handle differently formatted video signals such as high definition still video signals and animation video signals, has been disclosed in Japanese Patent Application Disclosure Gazette (kokai) No. HEI. 4-323973 whereby means for handling a plurality of pictures is used in the imaging part which changes over between an animation picture and a high definition still picture.
Since the above prior art has required an input of still video signals as a precondition, the prior art could have not accomodate the input of animation video signals. To enable the input of animation video signals, a high speed analog to digital converter and a signal processing circuit which requires high speed operation have been required for inputting high definition still video signals with high frequencies. Therefore, there have been problems such as an increase of power consumption of circuit elements for high speed operation and the expansion of the scale of various circuits along with use of high speed devices, such as ECL (Emitter Coupled Logic Circuit).
In a conventional method which has carried out sampling for each picture element by directly using a picture element clock as a sampling clock for the analog to digital converter, the sampling circuit has been required to operate at a high speed for high definition still video signals. Alternatively, in the case of a method for sampling the signals in a plurality of fields or a method for sampling the signals by means of a plurality of analog to digital converters, low frequency animation video signals could not be processed even though high frequency high definition still video signals could be processed. In addition, in the method for sampling the signals by using a plurality of analog to digital converters typically, the analog to digital converters have respectively different characteristics and therefore it has been impossible to avoid deterioration of the image quality with such as arrangement.